1. Filed of the Invention
The present invention relates generally to diagnosing problems in electrical circuits, and more particularly to a method of monitoring changes in electrical characteristics for diagnosing problems prior to component or system failure. The present invention specifically relates to diagnosing problems in an electrical system by monitoring changes in nonlinear characteristics.
2. Description of the Background Art
Linearity is a desirable characteristic for electrical components such as amplifiers, filters, transducers, digital-to-analog converters, and analog-to-digital converters. For instrumentation applications, the non-linearity represents an error or deviation from an accurate value. In audio or signal processing applications, the non-linearity generates harmonic and intermodulation distortion. Such harmonic and intermodulation distortion may mask desired components of a signal being processed. For example, delta-sigma digital-to-analog and analog-to-digital converters are capable of providing precision greatly in excess of sixteen bits. At the higher resolution, non-linearity becomes significant with respect to the least significant bit of resolution.
Although components can be designed, fabricated, and tested or calibrated to have a specified linearity, the linearity can degrade with time or due to abnormal operating conditions or stress placed on the components. For example, excessive power dissipation of an on-chip voltage regulator or power driver may cause a thermal protection circuit to limit current to the voltage regulator or power driver. This current limitation may cause severe distortion of a signal being processed by the electrical system.
Drift in the nonlinear characteristics of components in an electrical system can be corrected by periodic calibration of the system. However, such periodic calibration may tend to mask the symptoms of a more serious problem that may lead to a catastrophic system failure. Therefore, there is a need for diagnosing problems that cause changes in the nonlinear characteristics of components in an electrical system.